1. Field of the Invention
This invention relates to an electrophotographic apparatus, and more particularly to an electrophotographic apparatus in which a spacer member of a toner feed member is brought into contact with the surface of an electrophotographic photosensitive member so that the electrophotographic photosensitive member and the toner feed member can be positionally adjusted to each other. This invention also relates to a process cartridge that can be detachably mounted on the electrophotographic apparatus.
2. Related Background Art
Electrophotographic apparatuses such as copying machines and printers comprise an electrophotographic photosensitive member around which a charging means, an exposure means, a developing means, a transfer means, a cleaning means and so forth are provided. In particular, in the step of development where toner particles are made to adhere to the photosensitive member in accordance with electrostatically charged images formed on its surface, the gap between the toner feed member having toner particles and the photosensitive member has a very great influence on the images. This gap must be of an appropriate extent and also be uniform. If this gap is too wide, the toner adheres to the photosensitive member with difficulty to cause a decrease in image density. If on the other hand it is too narrow, the toner adheres to the photosensitive member with ease to make fine-line images thick, or the toner adheres to areas that should not undergo development, to cause fog.
In particular, in the case of what is called jumping development, the gap between the surface of the photosensitive member and the surface of the toner feed member must be kept more uniform since any variations of the gap between them has a great influence, as disclosed in Japanese Patent Application Laid-open No. 54-42141 and No. 55-18659.
As a method for positionally adjusting the toner feed member and the photosensitive member, there is a method in which a toner feed member is provided with, for example, spacer rolls made of resin, serving as a spacer member, and the spacer member is brought into contact with the surface of the photosensitive member.
In this method, however, the spacer member tends to damage a surface layer of the photosensitive member to cause separation of its photosensitive layer from its support. This tends to more remarkably occur when the peripheral speed of the toner feed member is set higher than the peripheral speed of the photosensitive member in order to increase toner density.
Of course, the spacer member may be so designed as to be brought into contact with areas outside the area in which the photosensitive layer is formed. In such an instance, however, it becomes necessary as a matter of course to make the support of the photosensitive member longer. This undesirably makes the whole apparatus larger in size. In addition, the toner tends to adhere to the portion where the spacer member is brought into contact and also it is difficult to clean such a portion, tending to cause faulty images.
As image quality has been made increasingly higher in recent years, studies have been conducted to make toners have a smaller particle diameter, to make drive systems have a smaller pitch non-uniformity and also, in printers to which images are inputted according to digital signals, to make picture element density higher. In such electrophotographic apparatuses, images are more remarkably affected unless the gap between the toner feed member and the photosensitive member is uniform.